Epidemiological Analysis of Notified Measles Cases and Review of Surveillance System During an Outbreak in Tabuk, Saudi Arabia

Abstract

In response to a measles outbreak occurred in Tabuk, Saudi Arabia, we conducted a case-based active-surveillance, and analyzed all surveillance data to identify the epidemiology of notified measles cases and to review the surveillance system. Suspected and confirmed measles cases were defined according to World Health Organization (WHO) guidelines. Household-based investigation was conducted for all suspected cases using standard measles notification form. Enzyme-linked immunosorbent assay was carried out on serum samples collected from all suspected cases to detect measles specific immunoglobulin M (IgM) antibodies. Surveillance system was assessed by preselected performance indicators consistent with WHO guidelines. Logistic regression was used to calculate crude and adjusted odds ratios from the surveillance data. Of 242 suspected measles cases notified between 3rd and 48th calendar weeks of the study-year, laboratory result was IgM-positive for 46% cases, IgM-negative for 49% cases, and unknown for 5% cases. Suspected and confirmed cases separately showed urban-predominance (>77%), male-majority (>51%), and high-proportion among Saudis (>92%). The highest proportion (93%) of suspected cases that received "at least one dose" of measles-containing vaccine (MCV) was found among those aged 12-17 years, whereas the lowest proportion (17%) was observed among the adult individuals (> or =18 years). Elderly (> or =18 years) individuals were significantly less likely to be vaccinated than younger (1-5 years) children (adjusted odds ratio [OR] = 15.92, 95% confidence interval [CI] = 4.82-52.56). The vaccine failure rate for "at least one dose" of MCV was 35%. The individuals vaccinated with "at least one-dose" of MCV were at 3.6 times lower risk of contracting measles than the nonvaccinated group (adjusted OR = 3.6, 95% CI = 1.55-8.38). Of five surveillance performance indicators, three were found as per WHO target. More efforts are essential to prevent future outbreaks and to reach the goal of measles elimination in the country.